A platen supports a workpiece for treatment by a processing tool. The platen may be an electrostatic platen that clamps the workpiece to the platen with electrostatic forces. The platen may also be a mechanical platen that clamps a workpiece with mechanical forces. The platen has a clamping surface that supports the workpiece. The workpiece may include, but not be limited to, a semiconductor substrate, a solar cell, a polymer substrate, and a flat panel. A platen may be used in many differing types of processing tools including, but not limited to, an ion implanter, a deposition tool, and an etch tool.
The clamping surface of the platen ideally has a high level of flatness. However, different conditions such as operating temperature may adversely impact the flatness of the clamping surface. For example, some electrostatic platens may be fabricated of different layers that are joined by a bonding agent such as epoxy. The different layers may have a different coefficients of thermal expansion (CTE) so that they expand and contract at different rates depending on the temperature.
FIG. 1 illustrates a cross sectional view of a platen 100 having clamping layer 102 a support layer 104. In one instance, the clamping layer 102 may be fabricated of a ceramic and the support layer 104 may be fabricated of aluminum. The platen 100 may be domed 100a or bowed 100b relative to treatment 106, e.g., by an ion beam in one instance. This curving of the platen may degrade results from the processing tool having such a platen.
In one instance, the processing tool may be a beam line ion implanter that treats a workpiece with an ion beam. For an angle sensitive application, any substantial deviation of the clamping surface of the plate from ideal flatness may degrade results. For example, one such application is a channeling ion implant into a semiconductor wafer workpiece. The semiconductor wafer may be fabricated of silicon and the crystalline lattice of the silicon may be oriented to promote channeling. If the angle of incidence varies slightly from a desired angle, the amount of channeling may be adversely reduced. The reduction in channeling is typically exacerbated at higher ion beam energies. Controlling the angle of incidence also helps to improve uniformity of the dose into a semiconductor wafer or other workpiece.
Accordingly, it would be desirable to provide an apparatus and method to control the flatness of the platen which overcomes the above-described inadequacies and shortcomings.